The present invention relates to a reconfigurable add-drop multiplexers. The invention also relates to a wavelength dependent cross-connects.
Significant increases in the bandwidth of an optical transmission system can be obtained by combining multiple signals of different wavelengths using wavelength division multiplexing (WDM). A key element in an optical network utilising wavelength division multiplexing is the so called xe2x80x9cadd-dropxe2x80x9d multiplexer which performs the function of adding and removing signals from the main multiplexed signal.
Add-drop multiplexers are well known in the art, and usually include a series of input and output ports. In particular, there is provided an input port for inputting the original WDM signal, an output port for outputting the resultant WDM signal from any add or drop function performed by the multiplexer, an add port for adding a signal of a specific wavelength to the outgoing WDM signal, and a drop port for removing a signal of a particular wavelength from the incoming WDM signal.
As with any optical component, it is desirable to manufacture as compact and inexpensive a device as possible.
An object of the present invention is to provide for an improved form of add-drop multiplexer providing a high level of flexibility and compactness.
In accordance with a first aspect of the present invention, there is provided an optical multiplexer device comprising: a first optical input channel; a second optical input channel; an optical output channel; a first series of polarization manipulation elements inconnected to the first and second input channel, the elements manipulating the polarisation state of light emitted from either the first or second input channel; a wavelength selective filter adapted to transmit first predetermined wavelengths and reflect second predetermined wavelengths emitted from the first and second optical channel; a second series of polarization manipulation elements for manipulating the first predetermined wavelengths; wherein input light from the second optical input channel having third predetermined range of wavelengths is combined with light emitted from the first optical input channel at the optical output channel. Preferably, light from the first optical input channel having the third predetermined range of wavelengths can be separated from the light transmitted at the optical output channel.
The second series of polarization manipulation elements preferably can include a variable polarization manipulation element having at least two states, and when in the first state: input light from the first optical input channel having the third predetermined range of wavelengths can be separated from the light transmitted at the optical output channel and input light from the second optical input channel having the third predetermined range of wavelengths can be combined with light emitted from the first optical input channel at the optical output channel; and when in the second state: input light from the first optical input channel can be transmitted substantially unaffected to the optical output channel. The variable polarization element can comprise a Faraday rotator. Ideally, the light separated from the first optical input channel can be output at a second optical output channel.
Further, the device also preferably includes a first mirror device for reflecting light emitted from the second series of polarisation manipulation elements back through the second series series of polarisation manipulation elements and the, first series of polarisation manipulation elements and the reflected second predetermined wavelengths are preferably also subsequently transmitted through the first series of polarization elements.
The first optical input channel, the second optical input channel and the optical output channel can comprise spaced apart, adjacent optical fiber devices.
In accordance with a further aspect of the present invention, there is provided a method of adding and removing predetermined wavelengths to an input optical signal so as to produce an output optical signal, the method comprising the steps of: (a) initially separating orthogonal polarisation states of the input signal to produce a separated input signal; (b) filtering the separated input signal so as to extract the predetermined wavelengths from the input signal producing a filtered separated input signal; (c) combining a desired wavelength output signal spanning the predetermined wavelength range with the filtered separated input signal to produce a separated output signal; (d) combining the polarisation states of the separated output signal to produce an output signal; (e) emitting the output signal.
The step (b) further can comprise rotating the polarisation state of the predetermined wavelengths and the desired wavelength output signal, the rotation being one of at least two magnitudes and when at a first magnitude the method provides the functionality of an add-drop multiplexer.
In accordance with a further aspect of the present invention, there is provided an optical add drop multiplexer for adding or removing at least one optical signals from a plurality of multiplexed optical signals, each of the optical signals having a unique wavelength, the multiplexer including a first and second input ports for receiving at least one inputted optical signal, and a first and second output ports for outputting at least one optical signal, wherein the multiplexer additionally preferably can include, a plurality of reciprocal optical crystal elements, a wavelength sensitive mirror, a second mirror, a least one rotator element, between the wavelength sensitive mirror and the second mirror; wherein, optical signals not reflected by the wavelength sensitive mirror are transmitted through the wavelength sensitive mirror, thereby separating the optical signals into reflected optical signals and transmitted optical signals, and wherein the transmitted optical signals are reflected by the second mirror and recombined with the reflected optical signals before the being coupled into at least one of the outputs. Various devices utilising the multiplexer can also be constructed.
In accordance with a further aspect of the present invention, there is provided in a tunable add drop multiplexer comprising: an input port and an output port; at least one wavelength output port; a tunable wavelength selection unit having a first control input for selecting and separating a first range of wavelengths from a groups of wavelengths; a input/output mode operation unit including a spatial light translation means for spatially translating light input from the input port to at least two separate locations; a method of tuning the multiplexer to add or drop a particular range of wavelengths comprising the steps of: (a) activiating the input/output mode operation unit to translate light input from the input port to the output port; (b) tuning the wavelength selection unit to select a predetermined range of wavelengths; (c) reactiviating the input/output mode operation unit to translate light input from the input port to the wavelength selection unit with the wavelength selection unit extracting the predetermined range of wavelengths from the input light and forwarding the remaining wavelengths to the output port.
The input/output mode operation unit preferably can include a non-reciprocal light polarisation rotation element coupled with at least one polarisation sensitive spatial translation element and the activiating and reactivating steps can include setting the non-reciprocal light polarisation rotation element to at least two separate states of rotation so as to thereby cause the polarisation sensitive spatial translation element to translate the light to two separate spatial positions.
The two separate spatial postions can include a first fully reflective mirror surface and a second partially reflective mirror surface.
The wavelength selection unit preferably can include a mirror having controllable external wavelength filtering characteristics.
In accordance with a further aspect of the present invention, there is provided an add/drop multiplexor comprising: input and output ports; a first polarisation separation means for spatially separating polarisation states emitted from the input port; a polarisation alignment means for aligning the separated polarisation states so as to produce aligned polarisation states; a first reciprocal rotator for rotating the aligned polarisation states in a reciprocal manner to produce first rotated polarisation states; a non-reciprocal rotator for rotating the first rotated polarisation states in a non-reciprocal manner to a degree determined by an input control to produce second rotated polarisation states; a first focussing element for focusing the second rotated polarisation states; a second polarisation separation means for spatially translating predetermined portions of the second rotated polarisation states to produce translated polarisation states; a second reciprocal rotator for rotating the translated polarisation states in a reciprocal manner to produce third rotated polarisation states; a third polarisation separation means for spatially translating predetermined portions of the third rotated polarization states to produce second translated polarisation states; a reflective filtering element having a first surface area substantially reflecting all the second translated polarisation states and a second surface area substantially reflecting a first range of wavelengths whilst transmitting a second range of wavelengths; a second focussing element for focusing the second range of wavelengths; a second reciprocal rotator for rotating the aligned polarisation states in a reciprocal manner to produce fourth rotated polarisation states; a fourth polarisation separation means for spatially translating predetermined portions of the fourth rotated polarisation states to produce third translated polarisation states; a drop port and an add port for droping the second range of wavelengths at the drop port and adding the second range of wavelengths to the reflected first range of wavelengths at the output port.
In accordance with a further aspect of the present invention, there is provided an optical demultiplexer for separating at least one candidate wavelength division multiplexed channel from a series of other channels, the multiplexer comprising: an input and output waveguide; a third demultiplexing channel waveguide; a first bypass unit connected to the input waveguide and having a bypass control input and projecting light emitted from the input waveguide to one of at least two spatial positions depending on the state of the bypass control input; a filter unit located at a first one of the two spatial positions, the filter unit optically separating the candidate wavelength channel from the series of other channels and transmitting the series of other channels to the output waveguide; an output transmission unit located at a second one of the spatial positions and transmitting all of the series of channels to the output waveguide.
Preferably, the filter unit includes variable filter properties which can be varied in accordance with a filter control input so as to select different members of the series for outputting on the demultiplexing channel waveguide.
Ideally, the first bypass unit includes a polarisation rotation element interconnected to the bypass control input which rotates the light emitted from the input waveguide by an amount determined by the bypass control input.
Further, the first bypass unit can include a non reciprocal polarisation rotation element interconnected to the bypass control input and wherein the output transmission unit transmits the series of channels to the output waveguide through the non reciprocal polarisation rotation element. The output transmission unit can comprise a mirror for reflecting light transmitted through the first bypass unit back through the first bypass unit and towards the output waveguide. Ideally, the input and output waveguides are spaced adjacent one another and the filter unit can comprise a wavelength selective mirror.
In accordance with a further aspect of the present invention there is provided an optical multiplexer comprising for adding at least one candidate wavelength division multiplexed channel to a series of other channels, the multiplexer comprising: an input waveguide; a third multiplexing channel waveguide for inputting the at least one candidate wavelength division multiplexed channel; a first bypass unit connected to the input waveguide and having a bypass control input and projecting light emitted from the input waveguide to one of at least two spatial positions depending on the state of the bypass control input; a filter unit located at a first one of the two spatial positions, the filter unit optically combining the candidate wavelength channel from the third multiplexing channel with the series of other channels and transmitting the resulting series channels to one of at least two spatial position depending on the state of the bypass control input; and an output waveguide located at one of the at least two spatial positions.
In accordance with a further aspect of the present invention, there is provided an optical add and drop multiplexer for separating at from a series of other channels, whilst simultaneously adding at least one substitute candidate wavelength division multiplexed channel to the series of other channels to provide a resulting series of output channels, the multiplexer comprising: an input and output waveguide; a third add channel waveguide for inputting the at least one candidate wavelength division multiplexed channel; a fourth drop channel waveguide; a first bypass unit connected to the input waveguide and having a bypass control input and projecting light emitted from the input waveguide to one of at least two spatial positions depending on the state of the bypass control input; a filter unit located at a first one of the two spatial positions, the filter unit optically separating the candidate wavelength channel from the series of other channels and further combining the candidate wavelength channel from the third multiplexing channel with the series of other channels and transmitting the resulting series channels to one of at least two spatial positions depending on the state of the bypass control input, with the output waveguide being located at one of the spatial positions; and an output transmission unit located at a second one of the spatial positions and transmitting all of the series of channels to the output waveguide.